Method for the neutralization of acid sludges



Feb. 2, 1943 F. l. DU PONT ET AL 2,309,633

METHOD FOR THE NEUTRALIZATION OF ACID SLUDGES Filed May 9, 1940 2 Sheets-Sheet l 29% WW5 y M w m 2 my .P/W

Feb. 2, 1943 F. l. DU P'ONT ET AL METHOD FOR THE NEUTRALIZATION OF ACID SLUDGES Filed May 9, 1940 2 Sheets-Sheet 2 fi'r rtg'r s Zo a l 3S Mm; a F ou//ze 5/ W Y% 4r a m/5X5.

Patented Feb. 2, 1943 METHOD FOR THE NEUTRALIZATION OF ACID SLUDGES Francis I. Du Pont, Wilmington, DeL, and Willing B. Foulke, Media, Pa, assignors to Delaware Chemical Engineering Company, Wilmington, Del., a corporation of Delaware Application May 9, 1940, Serial No. 334,114

6 Claims. (01. 196148) This invention relates to an improved method for the neutralization of acid sludges, in particular those acid sludges obtained in the ordinary sulphuric acid refining of uncracked mineral oil sludges with an excess of neutralizing agentQ preferably by boiling the sludges with solutions or suspensions of neutralizing agent, and then subject the organic material separated to vacuum distillation.

The practice in actual commercial use of the Rostler and Mehner process is to introduce into a steam jacketed tank provided with an agitator and capable of being closed to hold pressure, a certain amount of the acid sludge and a calculated amount of magnesium oxide suspended in a definite amount of water. They have adopted the plan of introducing the whole amount of sludge required for a charge of the jacketed tank, but only about one-fourth of the amount of magnesia suspension that would be necessary to neutralize the acid sludge. Next the tank is closed and the agitator started. If considerable pressure, say 50 lbs. per square inch, is immediately developed this is evidence that the reaction has occurred with the evolution of sulphur dioxide and with the generation of steam by the heat from the reaction of neutralization. If this pressure is slow in making its appearance then steam pressure may be turned into the jacket in order that the higher temperature may start the reaction. When there is evidence of reaction, the pressure is released from the tank and another one-fourth of the magnesia added, the tank closed and the above process repeated. This is done four times, i. e. four batches of magnesia suspension added successively, making sure each time that evidence of the reaction is observed before the next batch is added.

While the term neutralization is in a sense correct, What happens is akin to a saponification, that is a breaking up of the sulphuric acid compounds with the formation of a sulphate of the neutralizing agent. The reason for the appearance of sulphur dioxide is probabaly due to the fact that compounds akin to sulphonic acids have been neutralized. 1

Whatever may be the actual scientific truth of the neutralizing reaction, it has been found that very much better results can be obtained if this neutralizationis effected at a temperature considerably above the boiling point of water. For this reason, in the Rustler and Mehner process the reaction is usually completed under a pressure of about lbs. sq. inch produced either by the heat of reaction or by heat from the steam jacket or both. The better results referred to are manifested in a higher yield of hydrocarbon product.

It has been found that the acid sludges obtained in the ordinary refining with sulphuric acid of uncracked mineral oil products, such as lubricating oil, are extremely sensitive from the standpoint of chemical activity, and that upon being heated to even relatively low temperatures, or upon mechanical agitation, they tend to undergo a reaction which is thought to be one of polymerization. In any event, whatever the character of the reaction, it serves to lower, or even eliminate entirely, the yield of valuable hydrocarbons that may be obtained from the acid sludges.

Thus, it has been found that in heating the acid sludges in question to such temperature that they may conventiently be piped and handled as a liquid, the sludges, tend to polymerize to a greater or less extent, withconsequent reduction in the yield of hydrocarbons that may be obtained. Also, the mechanical agitation caused by the flow of the acid sludges in question through pipes and conduits is in some instances sufficient to cause serious losses in the yield of hydrocarbons by effecting a partial polymerization of the sludges.

It has been further found that this tendency to polymerize is a characteristic only of the sludge itself, or, in other words, of the sulphuric acidhydrocarbon condensation product of which the sludge is chiefly composed. That is to say, once the sludge has been'neutralized so that the condensation product is split, and the hydrocarbons thus transferred into free form,'polymerization will not occur.

It is accordingly the purpose of the present invention to provide an improved method for the neutralization of these acid sludges obtained in the sulphuric acid refining of uncracked mineral oils, so that polymerization of the sludge prior to its neutralization may be to the greatest possible extent avoided and the yield of the desired hydrocarbon product made as large as possible.

The Rostler and Mehner procedure described above has several serious disadvantages which we will now describe.

As it is not possible to estimate how far the reaction has proceeded before the tank is closed, it is not possible to predict what pressure will be generated by the combined heating of the steam jacket and the heat generated in the neutralizing reaction. Therefore, it is not possible to subject the reacting mass to whatever definite temperature may be found best.

In addition to this there is a decided element of danger in conducting the neutralization as has heretofore been the practice.

The reaction accompanied by the generation of much heat takes place mainly after the jacketed tank is closed and sometimes the rise in pressure is very rapid-almost sudden.

We have been informed that in one case in Europe where this was being carried out, the sudden pressure developed was so great that a disastrous explosion occurred. Because of this danger Rostler and Mehner adopted the procedure described above using four batches.

In our invention this danger can be entirely avoided and the sludge can be subjected to whatever temperature is found best, with definite and invariable certainty. This should insure the best possible yield.

The manner in which this and other objects .of our invention are to be accomplished may best be seen by consideration of a preferred embodiment of our invention as shown in the annexed drawings, in which:

Figure 1 is an elevation, partly diagrammatic, of apparatus designed for use in accordance with our invention; and

Figure 2 is a similar view of a modified form of apparatus.

As shown in Fig. l, a preferred apparatus for use in accordance with our invention comprises a centrifuge A, provided with outlets for three separate components, a mixing tank B, a steam jacketed neutralizing tank C, a centrifugal or fan pump D, a positive displacement pump E of the cam or gear type, and associated conduits and valves as shown.

In carrying out the method of neutralization in accordance with this invention, crude acid sludge may be piped directly from the refinery through the conduit 1 to the centrifuge A, which should be located as near the source of acid sludge as possible. This sludge contains, in addition to the hydrocarbon-sulphuric acid condensation product, appreciable quantities of mineral oil which it was not possible to separate from the sludge previously, and of free sulphuric acid of about 65 to 75% strength.

In the centrifuge A, which may be a conventional centrifuge of the closed type provided with outlets for three separate components of difierent densities, the crude acid sludge entering through the conduit 1 is separated into mineral oil, which is discharged to storage through the conduit 9, free sulphuric acid, which is discharged into a separate storage tank through the conduit i I, and purified acid sludge comprising essentially the desired hydrocarbon-sulphuric acid condensation product, which is discharged through the conduit !3 to the inlet side of the pump E.

Prior to this separation in the centrifuge A, an aqueous suspension of a neutralizing agent, such as, for example, magnesium oxide, calcium oxide,

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etc., will be prepared in the tank B with the use of the agitator l5 driven from the pulley IT. This suspension having been prepared in the tank B, the valve [9 will be opened and the contents will be discharged into neutralizing tank C, after which the valve l9 will again be closed.

The neutralizing agent will be kept in suspension within the tank C by the action of the agitator I, driven from pulley 3, and the suspension will be brought to the desired temperature, for example, to a temperature within the range 250-300 R, by the introduction of steam into the jacket of the tank C through pipe 2|, condensate and excess steam being removed through the pipe 23. At the same time, the suspension of neutralizing agent will be caused to circulate within the tank C and through conduits 25, 21 and 29 by the action of the pump D.

When the contents of the tank C have been brought to the desired temperature, for example, 250-3G0 F. centrifuge A and pump E will be started, and acid sludge discharged from the centrifuge through conduit 13 will be fed by the pump E into the circulating stream of neutralizing agent at 3| against the pressure obtaining in the system.

In this manner the acid sludge, almost immediately upon being discharged from the centrifuge A and before being subjected to any substantial increase in temperature or the effects of mechanical agitation for any considerable period of time, will be admixed with the suspension of neutralizing agent, already brought to a temperature which will promote quick reaction, circulating through the system comprising the tank C, conduits 25, 21 and 29, and the pump D. In passing through the pump D an intimate and efficient admixture of the acid sludge discharged from the pump E and the suspension of neutralizing agent will be obtained, and the desired neutralization of the acid sludge and freeing of the hydrocarbon component thereof will be more readily effected.

During the neutralization procedure the temperature of the circulating suspension of neutralizing agent will be maintained at a desired point both by the heat developed in the reaction of neutralization and that imparted by the steam passing through the jacket of the tank C. The safety valve 5, connected with the interior of the tank C'through the pipe 6, will serve to prevent damage if the temperature obtaining within the system should rise too high. Thus, the safety valve 5 may be set at a steam pressure of 75 pounds per square inch.

When all the acid sludge discharged from the centrifuge A has been introduced into the system by means of the pump E, or when upon testing a sample withdrawn from the system through the try-cock 33, acidity develops, the centrifuge A and the pump E will be stopped and circulation continued through the tank C and pump D for such time as may be necessary to complete the neutralization of the acid sludge, for example, approximately one hour and a half. Then the valve 2'5 in conduit 31 will be opened. and valve 32- in conduit 29 closed, and the contents of the tank C discharged through conduit 3'! to a vessel in which the organic material can be separated from the aqueous layer and subjected to vacuum distillation in known manner.

Ordinarily the amount of neutralizing agent, as, for example, magnesium oxide, which will be made up into a suspension in the tank B for any particular run, will be determined by having a known amount of crude acid sludge in the vessel from which the centrifuge A is supplied through conduit 7, and calculating the amount of neutralizing agent, as, for example, magnesium oxide, which will need to be introduced into the tank C for the neutralization of the quantity of refined sludge that will be fed into the system from the centrifuge A. Alternatively, where it is not possible to determine the amount of acid sludge that may be introduced into the system accurately, small samples will be removed from the system from time to time through the try-cock 33, and tested with an indicator, such as, for example, Congo red. As soon as acidity in the test sample appears, the centrifuge A and the pump E will be stopped.

In Figure 2 there is shown a modified form of apparatus in which the conduits 25, 21 and 29 and pump D are dispensed with, and sludge is pumped by pump E directly from centrifuge A to tank C. This form of apparatus can be used only where plant arrangement makes it practicable to locate centrifuge A closely adjacent tank C, and for this reason the construction shown in Fig. 1 is more adaptable to plant design, since the centrifuge A may be located anywhere.

In carrying out the neutralization in the apparatus shown in Fig. 2, a suspension of neutralizing agent will be prepared in tank B and introduced into tank C as before. The suspension in tank C will then be heated to the desired temperature, of, for example, 250-300 F., and when this temperature has been reached, centrifuge A and pump E will be started and sludge fed into the tank 6 against the pressure there obtaining. Agitator I will be used to insure thorough and intimate admixture of the contents of tank C.

When neutralization is complete, which may be determined in the manner set out above, the centrifuge A and pump E will be stopped and the contents of tank discharged through conduit 4| by opening valve 43.

We wish to call attention to the fact that since the sludge is introduced slowly in a small stream and since the temperature condition is such that complete neutralization occurs at once there is no risk of a sudden rise in pressure, any rise in pressure occurring gradually. The pressure due to the heating from the chemical action of neutralization can be controlled by turning cold water into the steam jacket of the tank 0 or by diverting temporarily the stream of sludge entering C; preferably the former.

It will be appreciated that the details of apparatus and procedure heretofore set forth are merely illustrative of our invention, and that various modifications thereof may be made without departing from the scope of the invention.

What we claim and desire to protect by Letters Patent is:

1. The method of neutralizing an acid sludge obtained in the sulphuric acid refining of mineral oil products which comprises forming a liquid neutralizing medium, maintaining a circulating stream of said neutralizing medium, and introducing a stream of acid sludge to be neutralized into said circulating stream.

2. The method of neutralizing an acid sludge obtained in the sulphuric acid refining of mineral oil products which comprises forming a liquid neutralizing medium, circulating said medium through a system including a zone in which the medium forms a pool and flows therethrough at relatively low velocity, and a second zone in which the medium forms a stream and fiows therethrough at relatively high velocity, and introducing a stream of acid sludge to be neutralized into said circulating body of neutralizing medium as it flows through the said second zone.

3. The method of neutralizing an acid sludge obtained in the sulphuric acid refining of mineral oil products which comprises flowing said sludge through as short a conduit as is practicable to a locus of separation, separating free mineral oil and free sulphuric acid from the sludge in the locus, forming a liquid neutralizing medium, heating said neutralizing medium to a temperature adapted to effect rapid neutralization, and flowing the refined sludge through as short a conduit as practicable from said locus of separation into said neutralizing medium maintained at said temperature, while avoiding any substantial heating of said sludge prior to its contact with said neutralizing medium heated to said temperature.

4. The method of neutralizing an acid sludge obtained in the sulphuric acid refining of mineral oil products which comprises flowing said sludge through as short a conduit as is practicable to a locus of separation, separating free mineral oil and free sulphuric acid from the sludge in said locus, forming an aqueous suspension of magnesium oxide, heating said suspension to a temperature of from about 250 F. to about 300 F., and flowing the refined sludge through as short a conduit as practicable from said locus of separation into said suspension maintained at said temperature, while avoiding any substantial heating of said sludge prior to its contact with said suspension heated to said temperature.

5. The method of neutralizing an acid sludge obtained in the sulphuric acid refining of mineral oil products which comprises maintaining an aqueous neutralizing agent under pressure in a closed tank at a temperature substantially above the boiling point of water, and pumping into said tank against said pressure a stream of said acid sludge.

6. The method of neutralizing an acid sludge obtained in the sulphuric acid refining of mineral oil products which comprises maintaining an aqueous neutralizing agent under pressure in a closed tank at a temperature substantially above the boiling point of water, agitating the contents of the tank, and pumping into said tank against said pressure a stream of said acid sludge.

FRANCIS I. DU PONT. WILLING B. FOULKE. 

